Apparatus and method for energy storage

Abstract

An energy storage apparatus includes a first circuit containing a first phase change material, a second circuit containing a second phase change material, and a heat pump having a cold side heat exchanger thermally coupled to the first circuit and a hot side heat exchanger thermally coupled to the second circuit. The apparatus is operable in a charging mode, a storage mode, and a discharge mode. In the charging mode the heat pump is energized to cool the first phase change material and heat the second phase change material. In the storage mode the first phase change material is stored in a first storage vessel and the second phase change material is stored as a pressurized vapor in a second storage vessel. In the discharge mode vaporized first phase change material is expanded by a first expander, or the vaporized second phase change material is expanded by a second expander.

The invention claimed is: 
     
       1. An energy storage apparatus comprising:
 a first fluidic circuit containing a first phase change material, the first fluidic circuit including a first storage vessel and a first expander; 
 a second fluidic circuit containing a second phase change material having a boiling point greater than a boiling point of the first phase change material, the second fluidic circuit including a second storage vessel and a second expander; and 
 a heat pump having a cold side heat exchanger thermally coupled to the first fluidic circuit and a hot side heat exchanger thermally coupled to the second fluidic circuit, 
 the apparatus being operable in a charging mode, a storage mode following the charging mode, and a discharge mode following the storage mode; 
 wherein in the charging mode the heat pump is energized to cool the first phase change material and heat the second phase change material; 
 in the storage mode the first phase change material is stored in the first storage vessel and the second phase change material is stored as a pressurized vapor in the second storage vessel; and 
 in the discharge mode vaporized first phase change material is expanded by the first expander, or the vaporized second phase change material is expanded by the second expander. 
 
     
     
       2. The apparatus of  claim 1 , wherein the first fluidic circuit is arranged such that in the discharge mode or storage mode the first phase change material may be heated by ambient thermal energy or other auxiliary heat sources. 
     
     
       3. The apparatus of  claim 2 , wherein the first fluidic circuit is arranged such that in the discharge mode or storage mode the first phase change material may be vaporized by ambient thermal energy or other auxiliary heat sources. 
     
     
       4. The apparatus of  claim 1 , further comprising a thermal coupling arranged to transfer heat from expanded second phase change material to the first phase change material and cause the first phase change material to vaporize or be further heated. 
     
     
       5. The apparatus of  claim 1 , wherein in the charging mode, the heat pump is energized to condense the first phase change material. 
     
     
       6. The apparatus of  claim 5 , wherein in the storage mode the condensed first phase change material is stored as a liquid or a solid. 
     
     
       7. The apparatus of  claim 1 , wherein the first phase change material has a boiling point less than 40° C. at 1 bar. 
     
     
       8. The apparatus according to  claim 7 , wherein the first phase change material has a boiling point less than 0° C. at 1 bar. 
     
     
       9. The apparatus according to  claim 7 , wherein the first phase change material has a boiling point less than −10° C. at 1 bar. 
     
     
       10. The apparatus of  claim 1 , wherein the second phase change material has a boiling point less than 40° C. at 1 bar. 
     
     
       11. The apparatus of  claim 1 , wherein the second phase change material has a boiling point greater than 20° C. at 1 bar. 
     
     
       12. The apparatus according to  claim 11 , wherein the second phase change material has a boiling point greater than 25° C. at 1 bar. 
     
     
       13. The apparatus according to  claim 12 , wherein the second phase change material has a boiling point greater than 30° C. at 1 bar. 
     
     
       14. The apparatus of  claim 1 , wherein the first storage vessel is configured to change volume so as to maintain the first phase change material at a substantially constant pressure. 
     
     
       15. The apparatus of  claim 1 , wherein the second storage vessel is configured to change volume so as to maintain the second phase change material at a substantially constant pressure. 
     
     
       16. The apparatus of  claim 1 , wherein one or each of the first expander and second expander comprises an expander generator. 
     
     
       17. A method of operating an energy storage apparatus that includes first and second fluidic circuits and a heat pump; where the first fluidic circuit includes a first phase change material, a first storage vessel and a first expander; the second fluidic circuit includes a second phase change material, a second storage vessel and a second expander; the second phase change material having a boiling point greater than a boiling point of the first phase change material; and the heat pump having a cold side heat exchanger thermally coupled to the first fluidic circuit and a hot side heat exchanger thermally coupled to the second fluidic circuit; the method comprising:
 operating the energy storage apparatus in a charging mode by energizing the heat pump to cool the first phase change material and heat the second phase change material; 
 operating the energy storage apparatus in a storage mode by storing the first phase change material in the first storage vessel and storing the second phase change material as a pressurized vapor in the second storage vessel; and 
 operating the energy storage apparatus in a discharge mode by vaporizing condensed first phase change material and expanding the vaporized first phase change material in the first expander, or expanding the vaporized second phase change material in the second expander. 
 
     
     
       18. The method according to  claim 17 , wherein the step of operating the energy storage apparatus in the charging mode includes energizing the heat pump to condense the first phase change material. 
     
     
       19. The method according to  claim 18 , wherein the step of operating the energy storage apparatus in the storage mode includes storing the condensed first phase change material as a liquid or a solid in the first storage vessel. 
     
     
       20. The method according to  claim 17 , wherein the step of operating the energy storage apparatus in the charging mode includes energizing the heat pump to vaporize the second phase change material.